Interstitial pressure is a physiologic property of the fluids which occupy the interstitial space of normal and tumor tissues. Animal models have suggested that these pressures are extremely high in tumors and may present a significant barrier to the movement of chemotherapy and immunotherapy agents into a tumor nodule. This goal of this study is to measure the interstitial pressure of tumors in patients who are enrolled in immuno- or chemotherapy trials at the BRMP. Additional data on the histologic diagnosis, the size of the nodule and its response to treatment will be examined in relation to the interstitial pressure. Six patients have been evaluated thus far, pressures as high as 60 mmHg have been observed. The only responding lesion in which pressure was measured, was a melanoma with a pressure of 10 mmhg; this value was 5-fold lower than other non-responding melanoma nodules. No toxicities directly attributable to the measurement procedure have been seen.